mirror of
https://github.com/jkriege2/JKQtPlotter.git
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96 lines
3.6 KiB
C++
96 lines
3.6 KiB
C++
/*
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Copyright (c) 2008-2024 Jan W. Krieger (<jan@jkrieger.de>)
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last modification: $LastChangedDate$ (revision $Rev$)
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This software is free software: you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License (LGPL) as published by
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the Free Software Foundation, either version 2.1 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU Lesser General Public License (LGPL) for more details.
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You should have received a copy of the GNU Lesser General Public License (LGPL)
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#ifndef JKQTPCACHINGTOOLS_H
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#define JKQTPCACHINGTOOLS_H
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#include "jkqtcommon/jkqtcommon_imexport.h"
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#include <QReadWriteLock>
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#include <QReadLocker>
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#include <QWriteLocker>
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#include <functional>
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/** \brief this class can be used to implement a general cache for values
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* \ingroup jkqtptools_concurrency
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*
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* It is typically used to generate a static (ThreadSafe=true) of thread_local (ThreadSafe=false) cache inside a function.
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*
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* The class is parametrized by a key (TKeay) and value (TData) data type and receives (in the constructor) a functor that
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* calculates the data for a key. An additional template parameter ThreadSafe indicates (true|false) whether the class
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* is implemented in a thread-safe way (for static instances) or not (then it should be used as thread_local instances in a
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* multi-threaded environment or in a single-thread environment).
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*
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* The class member function get(key) returns a value for a given key, which is either taken from the internal cache,
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* or generated using the functor provided to the constructor. In the latter case the generated value is stored in the internal cache.
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*
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* Internally the cache maps TKey to TData, but the signature of the get()-function and the generator functor actually uses TKeyInSignature,
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* which may differ from TKey. The only limitation is that TKeyInSignature can be converted/assigned to a TKey
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*/
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template <class TData, class TKey, bool ThreadSafe=true, class TKeyInSignature=TKey>
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struct JKQTPDataCache {
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template <typename FF>
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inline JKQTPDataCache(FF generateData):
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m_generateData(std::forward<FF>(generateData))
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{
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}
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template<class... Args>
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inline TData get_inline(Args... args) {
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return get(TKeyInSignature(args...));
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}
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template <bool TSS=ThreadSafe>
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inline TData get(const typename std::enable_if<TSS, TKeyInSignature>::type& key) {
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const TKey cacheKey=key;
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QReadLocker lockR(&m_mutex);
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if (m_cache.contains(cacheKey)) return m_cache[cacheKey];
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lockR.unlock();
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QWriteLocker lockW(&m_mutex);
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if (m_cache.contains(cacheKey)) return m_cache[cacheKey];
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const auto newData=m_generateData(key);
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m_cache[cacheKey]=newData;
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return newData;
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}
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template <bool TSS=ThreadSafe>
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inline TData get(const typename std::enable_if<!TSS, TKeyInSignature>::type& key) {
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const TKey cacheKey=key;
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if (m_cache.contains(cacheKey)) return m_cache[cacheKey];
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const auto newData=m_generateData(key);
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m_cache[cacheKey]=newData;
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return newData;
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}
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private:
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QHash<TKey, TData> m_cache;
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mutable typename std::enable_if<ThreadSafe, QReadWriteLock>::type m_mutex;
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const std::function<TData(TKeyInSignature)> m_generateData;
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Q_DISABLE_COPY(JKQTPDataCache)
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};
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#endif // JKQTPCACHINGTOOLS_H
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